I. Field of the Invention
This invention pertains to medical devices, but more specifically, to a method for increasing the cardiac output of a patient suffering from congestive heart failure by stimulating the heart of the patient at multiple sites simultaneously.
II. Discussion of the Prior Art
Normally, impulses from the SA node affect contraction of the atria and then propagate to the AV node. The AV node, in turn, emits a second nerve impulse which affects contraction of the ventricles. These nerve impulses affect contraction, i.e., depolarization of the tissue of the heart, in a coordinated manner to circulate blood through the body. Cardiac pacers of the type herein described generally are useful for maintaining proper functional operation of a sick heart. Of many cardiac deficiencies which have in the past been diagnosed and treated, conduction difficulties have presented significant problems for which a pacer has been used for treatment. A particular conduction deficiency, known as AV branch block, inhibits the transfer of nerve impulses from the sinoatrial (SA) node to atrial-ventricular (AV) node. When a bundle block occurs, these nerve impulses are not properly transmitted from the SA node to the AV node and ventricles.
When this condition occurs, normal treatment is to employ a pacer which locks onto the rhythmic cycle of the atrial beating signal and supplies to the ventricles a stimulating impulse at a certain time thereafter to effect contraction of the ventricles. The time period between the occurrence of the atrial beat and the normal contraction of the ventricles is known as the A-V delay period. Generally, hemodynamic efficiency is somewhat dependent to the A-V delay period, thus the pacer must emit a stimulating pulse at a time to preserve an optimum A-V delay period.
Other forms of conduction deficiency, such as myocardial scarring and bundle branch block, cause slow conduction of nerve impulses, in which case, nerve impulses are indeed passed from the SA to the AV node, but in a time period which is slower than normal. The Q-R-S complex in this case would manifest itself in being very wide and hemodynamic efficiency also becomes lower than normal.
In each of the above-mentioned cardiac deficiencies, the heart does not contract in coordinated fashion. This uncoordinated movement increases depolarization time and reults in more inefficient pumping rather than a more coordinated and simultaneous ventricular depolarization. In essence, such conduction deficiencies result in asynchrony between the left and right ventricle.
Additionally, arrhythmias of the heart produce uncoordinated ventricular contraction that affects the hemodynamic efficiency of the heart. Specifically, the recent paper xe2x80x9cIncomplete Filling and Incoordinate Contraction as Mechanisms of Hypotension During Ventricular Tachycardia in Manxe2x80x9d, published in Circulation, Vol. 68, No. 5, in 1983, describes that left ventricular function is severely disturbed by the disorganization of wall motion in hearts undergoing ventricular tachycardias. Moreover, it was found that hearts with impaired functions show profound reductions in pumping ability due to incoordinate contraction of the ventricles. It appears reasonable to believe, therefore, that any abnormal functioning heart that requires pacemaking or which has QRS widening will have a better hemodynamic efficiency if both ventricles are paced to contract in coordination with each other. There have been systems developed in the past employing a plurality of electrodes attached to the heart for effecting stimulation of a plurality of regions of the heart. For example, the Funke U.S. Pat. No. 3,937,226 discloses a cardiac electrical stimulation defibrillation system including a plurality of electrode terminals connected in a spaced relation on the heart. The electrodes, which provide stimulating and sensing, are each connected to amplifiers. The amplifiers are connected to electronic control circuit means configured to cause stimulation of all of the electrode terminals simultaneously in response to a sensed depolrization signal on the heart by at least one electrode terminal. In addition, the electronic control circuit is provided with a multivibrator means to synchronize the stimulation signal with the Q-R-S complex. Although Funke does teach the concept of simultaneous stimulation of a plurality of spaced electrodes, he does not disclose its specific use as a method of improving the cardiac output of patients suffering from congestive heart failure, nor does he discuss the specific placement of the electrodes about the heart.
The Rockland et al U.S. Pat. No. 4,088,140 discloses a similar system to Funke""s although a specific use as a pacemaker is stated in the patent. Rockland, et al discloses a demand anti-arrythmia pacemaker including a plurality of sensing electrodes connected to the heart to sense ventricular depolarizations. Electronic circuitry is provided having two paths of operation. A first path provides stimulation to one area of the heart if depolarization of a naturally occurring heart beat fails to occur within a first predetermined time period. In this first path, it is stated that the circuitry acts as a pacemaker in the event of skipped natural heartbeats. A second path provides stimulation to a plurality of locations on the heart if a depolarization signal is sensed on the heart with a second predetermined time period. In this second path, it is stated that the circuitry acts as a synchronous multiple electrode pacemaker or a synchronous multiple electrode defibrillator. Although, one example of an electrode placed in the intraventricular section and others in a spaced relation on the heart ventricles is given, there are no teachings of the specific placement of the electrodes on the heart nor the improvement of cardiac output from a sick heart. In addition, the electrodes perform either stimulating or sensing, not both, therefore a large number of electrodes is required in this system.
The Tacker, Jr. et al and McCorkle U.S. Pat. Nos. 4,548,203, 4,458,677 and 4,332,259, respectively, disclose the specific placement of an electrode in or around both left and right ventricles of the heart. The Tacker, Jr. et al patent discloses the placement of a catheter having one electrode in the right ventricle and another outside the heart and a third electrode placed on the left ventricle. The catheter electrodes, each being paired with the left ventricular electrode, are pulsed in sequence with a predetermined time separation resulting in uniform current density delivered to the heart. However, this pulsing scheme and configuration is disclosed for use in a ventricular defibrillation device and not for cardiac pacing to improve cardiac output wherein a more precise synchronization of stimulation signals with the Q-R-S complex is required.
The McCorkle, Jr. patents disclose the specific placement of an electrode in the right ventricle and another electrode in the coronary sinus surrounding the left ventricle for connection to a pacemaker. However, there is no specific technique disclose of providing stimulating signals to the electrodes to perform a pacemaking function.
In light of the above difficulties and shortcomings of the prior art, an objective of the present invention is to provide a cardiac pacer for increasing hemodynamic efficiency of a heart experiencing a conduction deficiency.
Another objective of the invention is to ensure a more coordinated and simultaneous ventricular depolarization of both left and right ventricles of the heart.
A yet further objective of this invention is to provide a cardiac pacer suitable for being implanted in a manner so as to impose a minimal surgical risk during implantation thereof.
A further objective of this invention is to provide a method and apparatus of separately sensing and stimulating each ventricle of the heart in order for effecting simultaneous contraction automatically of both ventricles of the heart to narrow the QRS complex of a failing heart and thereby cause an increase in blood pressure and cardiac output.
The method of the present invention involves a procedure for pacing of the heart in a particular way so as to improve its contraction pattern, and thereby augment the movement of blood through the heart. Patients suffering from severe congestive heart failure, which is found not to respond well to conventional drug therapy and to have a conduction defect in the ventricle resulting in a widen Q-R-S complex have been aided by a pacing regimen in which stimulating pulses are simultaneously applied to both ventricles by way of a demand pacemaker or asynchronous pacemaker.
It is theorized that a considerable part of the hemodynamic impairment in refractory congestive heart failure with conduction defects is due to an incoordinate contraction of the heart, so that a part of the heart muscle contracts and balloons out the part that is not contracting. When the latter area of the heart muscle does finally contract, the former has relaxed, so that a large part of the blood volume is merely shunted back and forth within the heart rather than being ejected as would happen with a more coordinate contraction pattern.
To attain the foregoing and other objectives, the present invention comprises, a bi-ventricular cardiac pacer having detecting and stimulating circuits for effecting substatially simultaneous contraction of both left and right ventricles of the heart. In the preferred embodiment, the bi-ventricular pacer comprises ECG amplifier means for separately processing sensed cardiac signals from each of the right and left ventricles. The amplified sensed signals are used to determined where possible abnormal conduction delays exist on the heart and to activate an electrical stimulator for stimulating the appropriate abnormally functioning part of the heart. More specifically, the stimulator responds to the control circuit to issue stimulating pulses simultaneously to either the left or right ventricle, as appropriate. The stimulator may be of the demand type wherein pacing pulses are only issued in the absence of a normal Q-R-S complex for on or the other of the two ventricles (e.g., occasional bundle branch block or slow conduction), or the nondemand type wherein pacing pulses are always issued (e.g., permanent bundle branch block or slow conduction).
To convey and sense signals to and from the heart, the present invention includes a pacing lead assembly comprising first and second separate electrodes. The first electrode is preferably introduced through the superior vena cava into the right ventricle and the second electrode is introduced through the coronary sinus to the left ventricle. Both lead segments include a sensing and pacing tip electrode which serves to both sense a cardiac depolarization signal or to apply a stimulating pulse from an implanted pulse generator to the ventricle.
Additionally, to preserve a predetermined A-V delay period, additional atrial sensing electrodes may be placed on or around the atrial chambers of the heart and connected to the control circuit. The control circuit responds to the sensed atrial and ventricular depolarization signals to provide simultaneous ventricular contraction signals applied to the left and right ventricles following a preset A-V delay period.
The advantages of the present invention include a more precise and coordinated simultaneous ventricular depolarization of both the right and left ventricular to thereby increase hemodynamic efficiency of a patient experiencing congestive heart failure or weak contractions.
These together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawing forming a part hereof, wherein like numerals refer to like parts throughout.